Research

Electrical engineers at the California Institute of Technology (Caltech) have developed a remarkably small and inexpensive silicon microchip that generates and radiates terahertz (THz) waves in a relatively unexplored region of the electromagnetic spectrum — between microwaves and far-infrared radiation — and can penetrate various materials without the ionizing damage of X-rays.

Electromagnetic waves in the range from 0.3 to 3 THz can easily penetrate materials and not only render image details in high resolution but also detect the chemical fingerprints of pharmaceutical drugs, biological weapons or illegal drugs or explosives, for instance. Existing terahertz systems, however, are bulky, expensive and may require demanding operating environments (e.g., very low temperature). So the Caltech team set out to explore whether novel techniques could be used to push low-cost integrated silicon technology into the terahertz frequency range.

Caltech’s proof-of-concept terahertz imager chip demonstrates a new and efficient way to generate power at frequencies beyond what is traditionally known as the cut-off frequency of the technology. “The chip encompasses the whole system, including the onchip radiators, which send out the signals directly from the chip,” explains Kaushik Sengupta, PhD, a post-doctoral scholar in the Electrical Engineering Department at Caltech. “Traditionally, integrating antennas inside silicon has been difficult. We not only overcame that challenge, but also integrated an array of 2D elements that can electronically beam-scan.” Electronic beam-scanning is very fast, as it removes the necessity to mechanically move the transmitter towards different parts of the scene.

According to the scientist, who will join the electrical engineering faculty at Princeton University in February 2013, having solved the challenges of signal generation with enough power, radiation and beam-control, the chip could enable “development of terahertz technology for short-range ultrafast wireless communication, see-through imaging for homeland security and contraband detection, bio-molecular spectroscopy, noninvasive quality control and possibly medical imaging.”

Caltech’s innovation constitutes the world's first integrated terahertz scanning arrays. Says Sengupta: “The most exciting part is that we have demonstrated a methodology that has shrunk a system that can take up a small benchtop to a chip that is only 2.7mm in length and breadth, while dissipating an order of magnitude lesser power.”

Designing single integrated antennas that are efficient yet small enough to fit into a microchip has been a technological bottleneck for some time. The Caltech team’s paradigm-shifting approach was to deconstruct traditional small single antenna systems and recombine multiples of circuits, electromagnetics and antennas to invent a structure — dubbed “distributed active radiator” — that generates THz waves at the desired power. “When we combine multiples of such elements, placed rightly in the silicon chip, the entire system radiates out very efficiently at the desired directions,” Sengupta says. “This is just a starting point. We plan to take this forward to realize its full potential and also invent new technologies that can further technology development in this area.”